8. A 5 g marble is shot out of a toy vertically straight up using a spring. The spring must be compressed 8cm if the marble goes up to a height of 20m above the position on the compressed spring. a) What is the change in the gravitational potential energy of the system when the marble shoots up? b) What is the change in the elastic potential energy of the spring during it's launch of the marble? c) What i s the spring constant of the spring